A48.1

HCC Category Mapping

What This Code Means

Legionnaires' disease is a serious lung infection caused by Legionella bacteria, typically acquired from contaminated water sources like air conditioning systems or hot tubs. It causes pneumonia with fever, cough, and breathing difficulties.

Coding Tips

• •Legionnaires' disease is a reportable condition in most jurisdictions; verify reporting requirements in your facility's compliance protocols
• •Confirm the diagnosis is specifically Legionnaires' disease (A48.1) rather than Pontiac fever (A48.2), which is a milder form of Legionella infection

Clinical Significance

Legionnaires' disease is a severe atypical pneumonia caused by Legionella pneumophila, typically acquired from contaminated water systems (cooling towers, hot water systems, decorative fountains). It carries 5-10% mortality in community cases and up to 25-30% in nosocomial cases. It is clinically significant because standard beta-lactam antibiotics used for typical pneumonia are ineffective — Legionella requires macrolides or fluoroquinolones.

Documentation Requirements

• ✓Legionella urinary antigen test positive (serogroup 1) or respiratory culture/PCR positive for Legionella
• ✓Chest imaging showing pneumonic infiltrates (often rapidly progressive, multilobar)
• ✓Clinical features supporting Legionnaires' disease (high fever, GI symptoms, hyponatremia, elevated LDH, rhabdomyolysis)
• ✓Epidemiologic exposure to potential water source (hospital, hotel, cruise ship, spa)
• ✓Public health notification documentation as this is a nationally notifiable disease

Commonly Confused Codes